Essentially, Mr. Bloomberg bought his way to the chairmanship of the group of global city leaders Clinton founded in 2005. Clinton had widespread buy-in, but lacked reliable financing and an means of tracking emissions. Bloomberg promised $6 million a year from his foundation for each of the next three years. (The Times quoted an anonymous Clinton adviser saying, “‘What are we going to do, fight him? They have the money; the golden rule applies.’ As in, he who has the gold, rules.”) Bloomberg is bringing a coterie of advisers with him.

This week’s C40 meeting aims to put members on track toward measurable emissions reductions. The group is also expected to announce a new formal partnership with the World Bank, giving it that much more juice.

Although cities[4] occupy just 2 percent of the world’s land mass, they account for 70 percent of energy consumption and 70 percent of greenhouse gas emissions. They are also home to half of the world’s population. Because C40 members are elected officials, they can directly affect emissions.

“If you address the problems of the cities, there will be no need for China[5] and India[6] to sign onto some international accord,” said Kevin Sheekey, a former deputy mayor of New York and an adviser to Mr. Bloomberg. “And thank God, because that’s not going to get done. It’s time to say it.”